public class DayCode {    public static void main(String[] args) {        int[][] nums = new int[][]{{1, 2}, {3, 4}};        int r = 1;        int c = 4;        int[][] ans = new DayCode().matrixReshape(nums, r, c);        System.out.println("ans is " + Arrays.deepToString(ans));    }        /**     * https://leetcode-cn.com/problems/reshape-the-matrix/     * @param nums     * @param r     * @param c     * @return     */    public int[][] matrixReshape(int[][] nums, int r, int c) {        int m = nums.length;        int n = nums[0].length;        if (m * n != r * c) {            return nums;        }
        int[][] ans = new int[r][c];        int newX = 0;        int newY = 0;        for (int i = 0; i < nums.length; i++) {            for (int j = 0; j < nums[i].length; j++) {                ans[newX][newY] = nums[i][j];                newY++;                if (newY >= c) {                    newX++;                    newY = 0;                }            }        }        return ans;    }
    /**     * https://leetcode-cn.com/problems/reshape-the-matrix/     * @param nums     * @param r     * @param c     * @return     */    public int[][] matrixReshape2(int[][] nums, int r, int c) {        int m = nums.length;        int n = nums[0].length;        if (m * n != r * c) {            return nums;        }
        int[][] ans = new int[r][c];        for (int x = 0; x < m * n; x++) {            ans[x / c][x % c] = nums[x / n][x % n];        }        return ans;    }}